Method of making springs



Nov. 6, 1945. c. A. HALLsTRoM ETAL 2,388,537

METHOD 0F MAKING SPRING Filed March 2o, 1942 A FuE- m.

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' Patented Nov. 6, 1945y 2,888,531 Manson oF MAKING srnmos Charles A. Hallstrom and Raymond E. Tibbetts, Worcester, Mass., assignors to The Americain f Steel and Wire Company of New Jersey, a cor poration of New Jersey Application Maren zo, 1942, semi No. 435,588

(ci. as m) 3 Claims.

The present invention relates to ,an improved method of making volute springs from fiat, ribbon-like steel strip, and is characterized by annealing one end of a steel spring blank so as to remove the temper therefrom, and subsequently cold forming the annealed end to conform to a curvature of predetermined radius and thereafter coiling the strip about an arbor corresponding to such radius so as to form a spring in which the innermost convolutions are devoid of dead or inactive coils.

Heretofore volute springs made by prior methods have usually had their innermost ends heated to a red heat and then coiled. 'I'his has resulted in the production of springs less effective than the springs which result from the practice of the present method, since in the conventional prior practice one or more turns a't the inner end` of the spring are dead or inactive. The primary object of the present invention is to overcome this inherent disadvantage in prior methods.

The above and related features of the inven- 'tion will be fully apparent from a consideration of the following detailed description, the accompanyingi drawing and the appended claims.

In the drawing:

Figure 1 is a perspective view of a length of ribbon-like spring steel strip after the same has been subjected to certain preliminary steps which characterize the present invention;

Figure 2 is a view of an arbor such as used in method;

Figure 3 is a view of the inner portion of a par- 1 tially formed spring wound on the forming arbor shown in Figure 2;

Figure 4 is a view of another forming arbor used in practicing the method;

Figure 5 is a side elevation of the type of arbor shown in Figures 2 and 4;

Figure 6 is a view of a completed spring made in accordance with the present invention and equipped with the usual retainer ring employed to'hold the spring in collapsed condition; and

Figure '7 is a view of the same spring shown in Figure 6 but with the retainer ring removed.

The primary purpose of the present invention is to provide an orderly method or improved procedure which will make available a volute spring having the greatest possible recoil and to increase the distance between the convolutions thereof. The invention will be described by way of example setting forth the exact steps followed in producing a spring such as shown in Figures 6 and '7.`

The spring which is illustrated in the expanded condition of Figure 7 is at least three and threesixteenths inches in outside diameter and each and every coil is characterized by an inherent ability to expand. To make suchv a spring we provide a forty-two inch length spring steel of ribbon-like form, the gauge of which may be, for example 21 gauge, and the width of which is three-fourths of an inch. The strip is of conventional spring steel analysis. Y

Both'ends of the ribbon-like strip will be perforated, one perforation serving to anchor the stock to the arbor, hereinafter referred to during the formation of the spring, and also to make attachment tothe device to Awhich the spring is to be associated, the perforation at the other end being similarly uilized for attachment in assembling the spring. The end of the strip which is to ultimately form the inner convolution of the spring is heat -treated in a gas annealing furnace so as to remove the temper therefrom. This conditions the steel of the spring stock so that the hardness of the first inch ranges from approxif mately 20 to 26 on the Rockwell C scale. The next two inches will range in hardness from 26 to 36 Rockwell C scale of the same scale. The next three inches will range in hardness from 26 to 48 Rockwell C scale. Beyond that the spring stock will all be of a hardness above 50 in the Rockwell C scale.

Thus it is apparent that the six inch length of the spring stock which is to ultimately form the inner convolutions will range in hardness from 20 to 48 -Rockwell C scale. The thus annealed end of the stock is placed in a press so as to form an arcuate bend such as shown in Figure 1 for the purpose of conforming the same to the radius of a cold forming arbor to be used in the next step of manufacturing the article. For example, the left end of the stock shown in Figure 1 is pressed to arcuate form corresponding approximately to three-eighths of an inch radius for subsequent engagement with the arbor of th configuration shown in Figure 2.

The arbor as indicated by the dimensions in Figure 2 is slightly out of round, the left half illustrated being a true semi-circle of .698 inch in diameter. The arcuate portion included between the 'radial lines a-b and c-d is of such radius that the diameter measured in any-portion of the upper right-hand quadrant will be .762 inch. The diameter as measured in the lower right-hand quadrant will be .742 inch. The arbor is provided with a hook-like projection i6 for engagement with the perforation I2 formed at the end of the blank strip B which is ponent part. Thereafter the spring is coiled tight on a backed of! arbor of the shape and dimensions shown in Figure 4. The diameter of this arbor at its largest point, as shown in Figure 4, is .821 inch. This arbor is given a suilicient number of turns to coil up the entire strip, with the exception of about three inches at the outer end, which portion extends out on a tangent to the outermost convolution of the spring. v After the spring is thus wound to the desired extent, a retainer ring I4 is slipped over it so as to facilitate assembling and handling.

If the entire forty-two inch length of the spring stock is initially coiled on an arbor, as in conventional prior practice, without performing the cold forming operation which characterizes the present invention, experience shows that it results in overstressing the tempered steel so that when the retainer is r'emoved the outside diameter falls below three inches and the spaces between the convolutions are correspondingly closer. It has also been found that there will be two to two and one-half inches of dead or inactive inner coils'at the center of the spring made by the prior methods, thus reducing the active working capacity thereof.

On the other hand, by the practice of the present invention involving cold forming a portion of the tempered steel in the spring, the stock can be wound on a larger arbor gauging .821, for example, such as shown in Figure 4. This reduces .the surface stress and results in a recoil of the spring to an outside diameter of from three and three-sixteenths inches to three and ilve-eighths inches with increased spaces between' the convolutions of the finished spring. Thus there is produced a spring such as shown in Figure 'l in whichall parts of the convolutions are alive and active. Otherwise expressed, there are no dead, inactive inner convolutions such as will be present in springs made by conventional prior practice.

From the detailed sequence of steps described, it is manifest that the method involves a series of essential steps for the production of volute springs comprising providing a length of ilat, spring tempered steel of ribbon-like form, perforating the ends thereof, annealing one end so as to remove or negative the effect of the spring temper of the steel, cold forming the said anhealedl end so as to make it conform to a predetermined radius, then engaging one perforated end with an arbor, such as shown in Figure 2, of a shape and size to correspond approximately to such radius, thereupon coiling the strip around the` arbor while the strip is cold, that is, at normal room temperature, and subsequently coiling assasav said end portion and approximately the remainder of the strip about a larger arbOl'. such as shmvn in Figure 4, so as to thus form a spring devoid of inactive coils at the center thereof.

While we have described quite precisely a preferred mode of operation with particular reference to specific dimensions corresponding to those use'd in' an actual reduction to practice, it is to be understood that the drawing and description are to be interpreted in an illustrative rather than a limiting sense since various modications may upon itself about an arbor of relatively small' diameter in the center of the spring, and thereafter coiling said end-length and the major portion of the remainder of said strip upon itself about an arbor of relatively larger diameter in the center of the spring, whereby there is produced a spring devoid of dead inactive coils at the center.

2. In the manufacture of springs, the method which comprises providing apiece of springtempered steel stock, subjecting a predetermined end-length thereof to an annealing treatment effective to gradually vary the hardness of successive portions of the stock from' approximately 20 to 48 on the Rockwell C" scale, cold forming said end-length by coiling it upon itself about an arbor of relatively small diameter in the center of the spring, and thereafter coiling said end-length and major'portio'n of the remainder of said stock about itself on an arbor of relatively larger diameter in the center of the spring whereby there is produced a spring devoid of dead inactive coils at the center.

3. In the manufacture. of springs, the method which comprises providing a piece of springtempered steel strip, subjecting an approximately 6inch end-length of the strip to an annealing treatment eil'ective to impart a hardness gradient thereto from approximately 20 to 50 on the Rock- Well C scale, shaping the softer extremity to an arc of predetermined radius of curvature. cold forming the strip by coiling said end-length upon itself about an arbor in the center of the spring having a volute cross-sectional contour of relatively small diameter, and thereafter coiling said end-length and the greater part of the remainder of the strip upon itself about a similar arbor of relatively larger diameter in the center of the spring, whereby there is produced a spring devoid of dead inactive coils at the center.

CHARLES A. HALLSTROM. RAYMOND E. TIBBETTS. 

